The purpose of the study was to examine the age-related differences in electromyographic (EMG) responses to transcranial magnetic stimulation (TMS) during functional isometric contractions in left and right hands. EMG responses were recorded from the first dorsal interosseous muscle following TMS in 10 young (mean ± s.e.m.; 26.6 ± 1.3 yrs) and 10 old (67.6 ± 2.3 yrs) right-handed subjects. Fifteen stimuli were delivered in random order at 80, 100, and 120% of resting threshold intensity for each isometric task, and muscle evoked potentials (MEPs) and silent period durations were obtained in the left and right hands in the same experimental session. The four isometric tasks performed were: (1) simple index finger abduction; (2) precision grip between index finger and thumb; (3) power grip involving all digits; and (4) scissor grip using spring-loaded garden shears. Subjects were provided with feedback of rectified and integrated EMG which was held constant at 5% of maximum EMG for all tasks. Normalised (relative to maximum M-wave) MEP area was 30% (P < 0.001) lower in the left (non-dominant) hand of old compared with young subjects for all tasks, whereas there was no age difference in the right hand. The duration of the EMG silent period was 14% (P < 0.001) shorter in old (150.3 ± 2.9 ms) compared with young (173.9 ± 3.0 ms) subjects, and the differences with age were accentuated in the left hand (19% shorter, P < 0.001). For all subjects, MEP area was significantly larger during the scissor grip compared with the other three tasks (10-12% larger) and this facilitation was due largely to the responses in the right hand of older adults. The longest EMG silent period was observed during the scissor grip in all subjects, and the largest task-dependent change in the silent period was again observed in the right hand of old subjects. We suggest that these differences in the corticospinal control in the left and right hands of older adults reflect neural adaptations that occur throughout a lifetime of preferential use of the hand for skilled (dominant) and unskilled (non-dominant) motor tasks.